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Thread: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

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    Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    I'm following up on the replacement of Porex by stainless mesh subtopic of this for sale thread, here. I did reach out to some people with lots and lots of positive experience doing deep dives with stainless mesh in place of Porex on a mk15.5 scrubber. However, my comments below relate specifically to my own experience replacing the Porex on a mk15 scrubber rather than a mk15.5.

    I ended up using two types of mesh in place of Porex: 1) coarse PVC, and 2) fine stainless. Pic given below. A relatively inflexible mesh is needed to keep the mesh, and in turn the sorb, from collapsing on the stainless scrubber ends (the semi-cylindrical indents in the stainless steel offset the Porex from the scrubber ends in the standard scrubber config, and thereby allow gas to access the entire scrubber surface). I chose PVC for this purpose rather than stainless steel as there was no requirement to shape or bend the mesh as it sits flat and it's quite inexpensive in comparison. The fine mesh is used to keep the sorb in place. **Note: Omitting the structural coarse mesh will lead to the fine mesh collapsing against the scrubber end surface with concomitant lowering of scrubber efficiency and an increase in WOB, and poor outcomes**

    As I was suggesting in the original thread where this came up, the situation is not unlike what is faced with radial scrubbers even though the mk15x scrubber is annular axial. Indeed, although the particular mesh and mesh sizes I used are not the same as the ones used in the Homebuilt Radial Meg Scrubber article by our own mk15x diver Skipbreather, I suspect that they would work fine.

    So, how is the WOB with the double mesh in place of Porex? My perception is that it is much better. It's not hard to do a simple dry land test. Put your lips on some Porex and breath through it. Do the same with the double mesh in an A/B test.

    Why even bother? I think Porex is a PITA. It's expensive, somewhat of an issue to source, readily clogs up, relatively fragile, and I don't like cleaning it with an HCl solution (yes, I said that) to restore it.

    Chris


    .IMG_2348.jpg

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    Supporting Member Sandy is on a distinguished road Sandy is on a distinguished road Sandy's Avatar
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    Love it. Im playing with stainless mesh at the moment. Ill add any non empirical data after a few dives.

  3. #3
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    I've got about 50 dives on the mesh modified scrubber at this point in water temperatures ranging from 47°F to 65°F.

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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    Hmmmmm.....

    As yet to be in focus question forming in my dark & twisted brain....

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    Supporting Member Sandy is on a distinguished road Sandy is on a distinguished road Sandy's Avatar
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    20151019_175341.jpg
    I used a fairly heavy stainless mesh with what I think I remember is 50% open rating. Im not worried about preserving my scrubber as "original" so I bonded the bottom layer to the scrubber with epoxy at the edges. I hope this helps keep it taught and prevents it from getting pushed into the base between the porex support ribs.
    I like the 50+ dive report. Nice.

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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    Really clean installation...

    So are you going to add foam to keep back small sorb grains/dust?

    The bit about not having to worry about keeping it "original" is classic...

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    Supporting Member Sandy is on a distinguished road Sandy is on a distinguished road Sandy's Avatar
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    I thought it was funny too...my wife says laughing at your own jokes is sad.
    Im using a new intersorb granular. Its almost dust free as far as I can tell. Ill just see how it goes. My dust check is to taste the condensation outside the scrubber after a half hour or so. Caustic is bad. Clean water is good. Salty is a different issue.

  8. #8
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    Both approaches very interesting. My inclination would be to experiment w/ combination of the two. What I mean by that: A coarse SS mesh stiff enough to stand off backed up by finer SS mesh to contain most of the 'sorb.

    When I look at the perforated PVC, I see the same thing I looked at closely when choosing materials for my radial scrubber, namely the % open factor. Measuring strictly by calibrated eyeball I'd call the PVC maybe 40%-ish open? Reduce each small hole of the PVC by a typical fine mesh of 50% open and you come up w/ 50% of 40%, or 20% open. The fact that it still breaths better than stock Porex is strong commentary on just how much original designers were willing to compromise WOB to gain some hydrophobic properties.

    I'll probably play w/ this at some point. My inclination will be to use something from this type of material in a 2x2 or 3x3:

    www.mcmaster.com/#catalog/121/438/

    as stand off mesh and something from here in a 40x40 or so:

    www.mcmaster.com/#catalog/121/436/

    to actually contain 'sorb.



    Regardless, can't argue w/ success. Very interesting thread.

  9. #9
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    Right. I went through all the mesh calculations too.

    Coarse stainless mesh, ~50% open.
    Coarse PVC mesh, ~40% open.
    Fine stainless mesh, ~50% open.

    Coarse stainless x fine stainless = ~25% open.
    Coarse PVC x fine stainless = ~20% open.

    Then factor in the stainless steel scrubber end cap "mesh" = nearly closed.

    Then factor in the equivalent mesh size of the sorb bed...

    Then...

    After mulling this, I came to the conclusion that the difference between 50 and 40 percent open for stainless vs. PVC was not something that was going to keep me from working with the less expensive material.

    I will say, though -- stainless steel is prettier than PVC.


    P.S.: The above analysis was comparing to the coarse stainless mesh in the "Homebuilt Radial Meg Scrubber" article, mcmaster no. 9358T151.
    Last edited by cys; 21st October 2015 at 01:35. Reason: added P.S.

  10. #10
    Supporting Member Sandy is on a distinguished road Sandy is on a distinguished road Sandy's Avatar
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    Re: Replacing Porex on a mk15 scrubber with PVC & stainless meshes

    Why not just coarse mesh on its own. (if its a really obvious reason with deadly results please just PM me to preserve my dignity on the forum)
    Sandy

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